1. Field of the Invention
The present invention relates to emergency stop circuits, in various machines such as robots or machine tools, for stopping operations thereof in an emergency.
2. Description of the Related Art
In a robot system, a safety measure is taken by surrounding the robot operating range with a fence so as not to let a person come into the robot operating area within the fence. The fence is provided with a door or the like, and when the door is opened, an emergency stop signal is output so as to stop the operation of the robot. Further, when an operation is taught to the robot, a teaching pendant is controlled to operate the robot, so the teaching pendant is provided with an emergency stop command button or the like, whereby the operation of the robot is stopped in an emergency by inputting an emergency stop signal through the button (see, for example, Japanese Patent Application Laid-open No. 10-217180).
Further, machine tools, injection molders or the like are also so configured that when a door of a processing unit or the like is opened, an emergency stop signal is output so as to stop the operation of the machine. That is, driving of the motor for driving an operable unit of the machine is stopped in an emergency to thereby stop the operation of the machine.
FIG. 7 shows an example of an emergency stop circuit used for a robot system or the like. In order not to damage the safety when one element of the emergency stop circuit is failed, the emergency stop circuit of the robot system is configured to detect emergency stop factors through independent two systems of emergency stop lines, composed of components with contacts such as relays, respectively. The machine is so configured that through a safety relay circuit 13 connected with the emergency stop circuit, power supply contacts Ca and Cb are controlled so as to interrupt power supply to the servo motor 12 for driving the machine to thereby cause the machine to be in the emergency stop state.
There are various matters serving as factors for stopping machines in an emergency, depending on machines. They include an emergency stop button and a door switch. FIG. 7 shows two emergency stop factors 14 and 15. The emergency stop factor 14 interrupts power supply to the relays R1a and R1b for the two systems of emergency stop lines A and B when the emergency stop button is manipulated. On the other hand, the emergency stop factor 15 opens a contact thereof by a relay, not shown, so as to stop power supply to the relays R2a and R2b. These relays or the like are provided as many as emergency stop factors. In FIG. 7, two emergency stop factors 14 and 15 are shown as examples.
In each of the two systems of the emergency stop lines A and B, normally-open contacts of the relays for respective emergency stop factors are connected in series. In the example shown in FIG. 7, on the line A, a normally-open contact r1a of the relay R1a, a normally-open contact r2a of the relay R2a, a normally-open contact r3a of a relay R3a operable by a command from the CPU 10, a normally-open contact k1a of a safety relay K1 in the safety relay circuit 13, and a safety relay K2 are connected in series, and a voltage is applied to either end of the series circuit. A normally-open contact k2a of the safety relay K2 is connected in parallel with the normally-open contact k1a of the safety relay K1.
Similarly, on the line B of the other system, a normally-open contact r1b of the relay R1b, a normally-open contact r2b of the relay R2b, a normally-open contact r3b of a relay R3b operable by a command from the CPU 10, a normally-open contact k1b of a safety relay K1 on the safety relay circuit 13, and a safety relay K3 are connected in series, and a voltage is applied to either end of the series circuit. A normally-open contact k3a of the safety relay K3 is connected in parallel with the normally-open contact k1b of the safety relay K1.
Relating to the contactor Ca, a normally-close contact k1c of the safety relay K1, a normally-open contact k2c of the safety relay K2, and a normally-open contact k3c of the safety relay K3 are connected in series, and a voltage is applied to the series circuit. Similarly, relating to the contactor Cb, a normally-close contact k1d of the safety relay K1, a normally-open contact k2d of the safety relay K2, and a normally-open contact k3d of the safety relay K3 are connected in series, and a voltage is applied to the series circuit.
The servo amplifier 11 is connected with a three-phase power source via contacts Ca1 and Cb1; Ca2 and Cb2; and Ca3 and Cb3, which are connected in series for respective phases. The contacts ca1, ca2 and ca3 are normally-open contacts, for respective phases, of the contactor Ca, and the contacts cb1, cb2 and cb3 are normally-open contacts, for respective phases, of the contactor Cb. Further, the normally-close contacts ca4 and cb4 of the contactors Ca and Cb, the normally-close contacts k2b and k3b of the safety relays K2 and K3, and the safety relay K1 are connected in series, and a voltage is applied to either end of the series circuit.
In FIG. 7, “DI” indicates a digital input element, and “DO” indicates a digital output element. The digital input elements DI constitutes a detecting means for detecting the states of respective contacts of the relays R1a to R3a and R1b to R3b operable by the emergency stop factors 14 and 15 and commands from the CPU 10.
At the time of power being supplied, the safety relay K1 operates to close the normally-open contacts k1a and k1b thereof, and to open the normally-close contacts k1c and k1d. If no emergency stop command is inputted from an emergency stop factor, the contacts r1a to r3a on the line A and the contacts r1b to r3b on the line B are closed so that the safety relays K2 and K3 are excited, and the safety relays K2 and K3 are self held via the contacts k2a and k3a. Due to the safety relays K2 and K3 being excited, the normally-close contacts k2b and k3b are opened, so that the safety relay K1 is non-excited. Thereby, the contact k1c to k3c are closed, and the contactor Ca is excited. Similarly, the contact k1d to k3d are closed, and the contactor Cb is excited. Consequently, the contacts of the contactors Ca and Cb are closed, so that the power is supplied to the servo amplifier 11 from the power source, whereby the servo motor 12 becomes operable.
If an emergency stop command is inputted due to any one of the emergency stop factors 14 and 15, or an emergency stop command is outputted from the CPU 10, and the contacts r1a to r3a or the contacts r1b to rb3 on either emergency stop line A or B are opened, the safety relay K2 and/or the safety relay K3 is non-excited, whereby the contactors k2c, k2d, k3c and k3d are opened and the contactors Ca and Cb are non-excited, whereby the contacts ca1 to ca3 and cb1 to cb3 are opened to thereby interrupt power supply to the servo motor 12. Consequently, operation of the servomotor 12 is stopped, and the machine is stopped in an emergency.
The conventional emergency stop circuit uses a safety relay circuit composed of safety relays in which operations of the contacts are assured, whereby specially-designed, expensive components must be used. Further, the circuit is complicated and a number of general components must be used as well. This causes an adverse effect on the cost and reliability.